Transforming growth factor- (TGF-) is a negative regulator of normal, benign and malignant prostate growth. While serving a growth-inhibitory/apoptotic role in the normal prostate, overproduction of TGF- 1 in the aging prostate contributes to the development of benign prostate hyperplasia (BPH) and prostate cancer. We previously established that activation of TGF-s signaling leads to apoptosis induction and loss of TGF RII receptor (T2RII) contributes to prostate tumorigenic growth. Overexpression of T2RII in human prostate cancer cells enables apoptosis-mediated-growth suppression in response to TGF- in vitro and in vivo. Using the LNCaP T2RII prostate cancer cells (androgen-sensitive and TGF- responsive) as a model, it was shown that TGF- 1 induces apoptosis and this effect was enhanced by androgens. Recent proteomic-based approaches identified two new intracellular effectors of TGF- pathway that act independent of Smads to regulate apoptotic outcomes in prostate cancer cells. In this proposal we hypothesize that TGF- 1 signaling via changes in Smad4-independent intracellular effectors and cross-talk with the androgen receptor (AR) regulates prostate growth, and functional inactivation of this network accelerates the manifestation of the malignant phenotype and tumor progression. The following four Specific Aims will test this hypothesis: Specific Aim 1 will characterize the functional involvement of Smad- independent signaling effectors, prohibitin and cofilin, as novel mediators of TGF- action in prostate benign and malignant epithelial cells. Specific Aim 2 will identify the significance of the androgen receptor (AR) in the signaling interaction between TGF-1 and androgens towards apoptosis and epithelial to mesenchymal transition (EMT) of prostate tumor epithelial cells. Specific Aim 3 will establish the role of cofilin as a novel regulator of the ability of prostate (stroma) fibroblasts to direct TGF- signaling, in the context of the tumor microenvironment. Specific Aim 4 will characterize the in vivo physiological consequences of a functionally impaired TGF- signaling on prostate growth, tumor initiation and progression using a conditional knockout mouse DNT2RII, to generate double transgenics upon crossing with the TRAMP transgenic mouse model. These studies will provide new insights into the mechanistic deregulation of TGF signaling network that contributes to prostate growth and tumor progression. Understanding how cells read TGF- will enable both the delineation of the transcriptional programs that mediate specific TGF- effects and provide a framework for defining the mechanism via which TGF- 1 growth inhibitory/apoptotic responses in normal, benign and pre-malignant prostate cells, might be selectively replaced by invasive and metastatic responses in cancer cells. PUBLIC HEALTH RELEVANCE: The long term objective of the application is to characterize the functional interplay between the TGF- 1 and androgen signaling pathways that independently of Smad effectors and in the context of tissue microenvironment contribute to deregulation of TGF 1 mediated effects on prostate growth during tumor initiation and progression. The application will also pursue the mechanism converting TGF- from a tumor suppressor in normal and benign prostate growth, to a tumor promoter in advanced metastatic cancer.